Python script for converting a private key from p, n and e values to a PEM private key format

pkeygen.py

#!/usr/bin/env python3


import sys
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa

from tpm2_pytss.internal.crypto import _MyRSAPrivateNumbers as MyRSAPrivateNumbers

nums = {
    "p" : None,
    "n" : None, 
    "e" : 65537
}

if len(sys.argv) < 3 or len(sys.argv) > 4:
    sys.exit("Expected 2 or 3 key value arguments like p=abcdef123 q=1234fde e=65537. Note e is optional and defaults to 65537")

for arg in sys.argv[1:]:
    k,v = arg.split('=')
    
    if k not in nums:
        sys.exit(f'Unknown key "{k}"')

    try:
        base = 16 if k != "e" else 10
        nums[k] = int(v, base)
    except ValueError as e:
        sys.exit(f'Expected key "{k}" as base: {base}')


pubnums = rsa.RSAPublicNumbers(e=nums["e"], n=nums["n"])
m = MyRSAPrivateNumbers(p=nums["p"], n=nums["n"], e=nums["e"], pubnums=pubnums)

pk = m.private_key()
pem = pk.private_bytes(encoding=serialization.Encoding.PEM,
                 format=serialization.PrivateFormat.TraditionalOpenSSL,
                 encryption_algorithm=serialization.NoEncryption())

sys.stdout.write(pem.decode())

sys.exit(0)